Ground or Strata Instability in Underground Mines and Tunnels

Transcription

1 H E A LT H & S A F E T Y AT WO R K HSWA AC T APPROVED CODE OF PRACTICE Ground or Strata Instability in Underground Mines and Tunnels SEPTEMBER 2016

2 ACKNOWLEDGEMENTS WorkSafe New Zealand (WorkSafe) would like to thank the members of the industry working group for their contribution to the development of this code. Our thanks also go to NSW Government Trade and Investment, Regional Infrastructure and Services; Safe Work Australia; Government of Western Australia Department of Mines and Petroleum; Open House Management Solutions, South Africa; Strata Control Technology, NSW, Australia; and the Health and Safety Executive (HSE), England for letting us use content from their publications.

3 NOTICE OF APPROVAL The code of practice for Ground or Strata Instability in Underground Mines and Tunnels sets out WorkSafe New Zealand s expectations in relation to identifying and controlling the work health and safety risks arising from mining and tunnelling operations, in order to help PCBUs and workers achieve compliance with the Health and Safety at Work Act 2015 and the Health and Safety at Work (Mining Operations and Quarrying Operations) Regulations WorkSafe New Zealand developed the code with input from unions, employer organisations, other key stakeholders and the public. Together with the right attitudes and actions of PCBUs and workers focused on improving health and safety practices at work places, the code will contribute to the Government s targets of reducing the rate of fatalities and serious injuries in the workplace by at least 25% by Accordingly, I Michael Allan Woodhouse, being satisfied that the consultation requirements of section 222(2) of the Health and Safety at Work Act 2015 have been met, approve the code of practice for Ground or Strata Instability in Underground Mines and Tunnels under section 222 of the Health and Safety at Work Act Hon Michael Woodhouse Minister for Workplace Relations and Safety 16 August 2016

4 FOREWORD As the Chair of the Board of WorkSafe New Zealand, I am pleased to introduce this approved code of practice for Ground or Strata Instability in Underground Mines and Tunnels. It was developed with input from our social partners, industry and public consultation. This approved code of practice will help duty holders comply with their requirement to provide healthy and safe work for everyone who works in this industry. It will also help make sure that other people do not have their health and safety adversely affected by the work conducted. A healthy and safe workplace makes good sense. An organisation with health and safety systems that involve its workers can experience higher morale, better worker retention, increased worker attraction and most importantly workers who return home to their families, healthy and safe, after they finish their work. Organisations benefit from having less downtime from incidents and higher productivity. An organisation known for its commitment to health and safety can benefit from its improved reputation. We must all work together to make sure that everyone who goes to work comes home healthy and safe. By working together, we ll bring work-related harm down by making sure that all work conducted is healthy and safe work. Professor Gregor Coster, CNZM Chair, WorkSafe New Zealand

5 TABLE OF CONTENTS PART A 01 INTRODUCTION What is the purpose of this code? What is the legal status of this code? How to use this code Roles and responsibilities Worker engagement, participation and representation Health and safety management system Hazards and risks Principal hazard management plan for ground or strata instability 16 PART B 02 CAUSES OF GROUND OR STRATA INSTABILITY AT THE OPERATION Identify the causes of ground or strata instability GEOTECHNICAL ASSESSMENT Requirement for a geotechnical assessment at mining and tunnelling operations Site characterisation Collection, analysis and interpretation of geotechnical data Re-using a geotechnical assessment Review of the geotechnical assessment DESIGN OF CONTROL MEASURES/SUPPORT METHODS TO AVOID GROUND OR STRATA INSTABILITY Design details and support methods Design methodologies used to determine ground support needed Design requirements for rock reinforcement systems Stope or pillar design requirements for coal and metalliferous mines Temporary and permanent ground support systems 37

6 4.6 Primary and secondary support systems Temporary support systems Shafts Continuous modelling and design verification 45 PART C 05 IMPLEMENTING THE CONTROL MEASURES Ground support/controls and excluded areas Application for construction or permit to tunnel Self-supporting mines or tunnels Installation training Scaling and barring down Installing temporary support Equipment used during installation Timing of support/reinforcement installation Support materials/consumable items Standard operating procedures Manager s support rules for installation Installing higher standards of support Inadequate ground or strata support Rock bolt integrity Lifting and suspension of equipment in rock bolted roadways or tunnels Withdrawal of support material MONITORING, INSTRUMENTS AND REPORTING Monitoring ground or strata instability Benefits of monitoring Monitoring plan Trigger Action Response Plans (TARPs) Selecting suitable monitoring methods and instrumentation Monitoring bolt integrity Geotechnical hazard zones hazard plans or maps Seismic monitoring Measurement of loads and deformation Ground or strata movement indicators 76

7 6.11 Crack monitoring Monitoring pillar and extraction sequence design coal mining Monitoring to detect goaf/waste fall precursors Monitoring for movement caused by tunnel development Regular examinations and shift reports GROUND OR STRATA FAILURE AND ACTIONS REQUIRED Report actual or suspected ground or strata failure EMERGENCY PREPAREDNESS Prepare for ground or strata instability emergencies 85 PART D 09 NOTIFIABLE EVENTS Notifiable events REVIEW AND AUDIT When to review the PHMP Auditing the PHMP Communicating changes from reviews or audits 93 PART E 11 GLOSSARY APPENDIX Example of a Trigger Action Response Plan (TARP) REFERENCES 107

8 TABLES 1 Requirements in this code 13 2 Terminology used to refer to support in coal mines, metalliferous mines and tunnels 37 3 Monitoring methods 68 4 Commonly used instruments 77 5 Some of the regular examinations required to be completed at mining or tunnelling operations 81 FIGURES 1 Development and maintenance of a ground or strata instability PHMP 18 2 Components of the geotechnical assessment and design outputs 26 3 Example of inrush control zone marked on a plan 36 4 How tensioned rock bolts clamp the strata 38 5 Rock bolts in a metalliferous mine or tunnel 39 6 Code green support plan 57 7 Code red support plan 58 8 Strain gauge 70 9 Example of hazard zones shown on a hazard map Example of a hazard map from an underground metalliferous mine Shear indicator Examples of convergence monitoring and measuring locations in a segmented tunnel lining and underground tunnel or roadway 78 KEY C M T Coal Metalliferous Tunnels

9 APART IN THIS PART: Section 1: Introduction

10 PART A 01/ INTRODUCTION IN THIS SECTION: 1.1 What is the purpose of this code? 1.2 What is the legal status of this code? 1.3 How to use this code 1.4 Roles and responsibilities 1.5 Worker engagement, participation and representation 1.6 Health and safety management system 1.7 Hazards and risks 1.8 Principal hazard management plan for ground or strata instability 10

11 SECTION 1.0 // INTRODUCTION The legislation that applies to this section is: Health and Safety at Work Act 2015 Section 22 Meaning of reasonably practicable Section 30 Management of risks Section 222 Approval of codes of practice Section 226 Use of approved codes of practice in proceedings Part 2 Health and safety duties Part 3 Worker engagement, participation, and representation Schedule 3: Clause 1 Interpretation mine operator Clause 2 Meaning of mining operation Clause 4 Meaning of tunnelling operation Clause 8 Power of health and safety representative to give notice requiring suspension of mining operation Clause 9 Power of health and safety representative to require mining operation to stop in case of serious risk to health and safety Clause 11 Competency and experience requirements for exercise of powers under clauses 8 and 9 Clause 19 Functions and powers of industry health and safety representatives Health and Safety at Work (Mining Operations and Quarrying Operations) Regulations 2016 Regulation 55 Risk assessment Regulation 60 Engagement Regulation 68 Content of principal hazard management plans Regulation 71 Principal hazard management plans for ground or strata instability Regulation 73(3) Consideration of whether inundation and inrush is a principal hazard Regulation 109 Worker participation practices must be documented Regulation 114 Mine operator must investigate reported hazard Regulation 115 Mine operator must advise mine worker of result of investigation Part 3 Health and safety management system The Health and Safety at Work Act 2015 (HSWA) is New Zealand s key work health and safety legislation. It sets out work-related health and safety duties that must be complied with. Health and safety regulations sit under HSWA, expand on the duties under HSWA and set the requirements for managing certain risks and hazards. 11

12 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS Approved codes of practice (codes) set out WorkSafe New Zealand s (WorkSafe) expectations about how duty holders are to comply with their legal duties under HSWA and related regulations. The relevant legislation for this code is: > > Health and Safety at Work Act 2015 (HSWA) > > Health and Safety at Work (Mining Operations and Quarrying Operations) Regulations 2016 (the MOQO Regulations). See WorkSafe s special guide Introduction to the Health and Safety at Work Act 2015 for more information on health and safety law. 1.1 WHAT IS THE PURPOSE OF THIS CODE? This code sets out WorkSafe s expectations for managing ground or strata instability in underground mining and tunnelling operations. It applies to all underground mining and tunnelling operations where ground or strata instability is a principal hazard. The code includes information on: > > causes of ground or strata instability > > geotechnical assessment > > design and implementation of control measures > > monitoring controls > > review and audit requirements. This information contributes to the contents of the ground or strata instability principal hazard management plan (PHMP). This code is for the site senior executive (SSE), mine operator, mine manager, and anyone else at the mining or tunnelling operation involved in managing the ground or strata instability principal hazard. This includes workers and other persons. 1.2 WHAT IS THE LEGAL STATUS OF THIS CODE? This code has been approved under section 222 of HSWA. It can be used in court as evidence of whether HSWA has been complied with. Courts may use this code: > > as evidence of what is known about the ground or strata instability principal hazard at an underground mining or tunnelling operation and how those risks may be controlled > > to decide what is reasonably practicable for managing the ground or strata instability principal hazard at an underground mining or tunnelling operation. Following the code may not be the only way of complying with HSWA and the MOQO Regulations. Other practices can be used as long as they provide a level of work health and safety equivalent to or higher than in this code, and comply with HSWA and the MOQO Regulations. For more information about the hierarchy of the legislation and the relationship with other guidance documents, refer to WorkSafe s special guide Introduction to the Health and Safety at Work Act See also WorkSafe s interpretive guidelines Developing a Ground or Strata Instability Principal Hazard Management Plan. 12

13 SECTION 1.0 // INTRODUCTION 1.3 HOW TO USE THIS CODE INTERPRETING THIS CODE Table 1 shows the terms used to describe the requirements in this code. TERM Must Needs to, or content written as a specific direction (eg Make sure the. ) Should May DEFINITION legal requirement that has to be complied with a practice or approach that has to be followed to comply with this code WorkSafe s minimum expectation (subject to the legal status of this code described in section 1.2) recommended practice or approach, not mandatory to comply with HSWA or this code permissible practice or approach, not mandatory to comply with HSWA or this code Table 1: Requirements in this code LEGISLATION At the start of each section in this code, the legislation that applies is listed in a box. For the full text see TERMS USED IN THIS CODE MINING AND TUNNELLING This code uses the terms mining operation and tunnelling operation even though the definition of mining operation in HSWA includes a tunnelling operation. This is to emphasise that parts of the code apply to both mining operations and tunnelling operations. Tunnel operator is used in this code to refer to the person responsible for the tunnelling operation and has the same meaning as mine operator under HSWA. COMPETENT PERSON Competent person means a person who: a. has the relevant knowledge, experience, and skill to carry out a task required or permitted by the MOQO Regulations to be carried out by a competent person; and b. has a relevant qualification evidencing the person s possession of that knowledge, experience, and skill or if the person is an employee a certificate issued by the person s employer evidencing that the person has that knowledge, experience, and skill. Other terminology used in this code is explained in the Glossary MINING OR TUNNELLING OPERATION TYPES This code applies to all underground mining and tunnelling operations. Where content is specific to a particular operation an icon is shown as follows: C M T Coal Metalliferous Tunnels 13

14 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS STANDARDS Use the most recent version of any standards referred to in this code, unless otherwise specified. Where applicable, and provided it does not contradict the legislation or requirements of this code, refer to BS 6164 Code of practice for health and safety in tunnelling in the construction industry for good practices in the construction of tunnels. 1.4 ROLES AND RESPONSIBILITIES HSWA defines the roles and responsibilities of different duty holders. These include persons conducting a business or undertaking (PCBUs), officers, workers and other persons at workplaces. See WorkSafe s special guide Introduction to the Health and Safety at Work Act 2015 for more information. Schedule 3 of HSWA and Part 2 of the MOQO Regulations set out the specific mining sectorrelated roles including mine operator, mine worker, SSE, mine manager, safety critical roles, and industry health and safety representative. All mine or tunnel operators must appoint a SSE and a mine or tunnel manager. The SSE is responsible for health and safety management and the mine or tunnel manager for the daily running of the mine or tunnel operation. Depending on the type of mining operation and the particular principal hazards other safety critical roles are required. For underground mining or tunnelling operations the SSE is required to appoint a number of safety critical roles. For more details, see regulations 28, 30, and WORKER ENGAGEMENT, PARTICIPATION AND REPRESENTATION All mining and tunnelling operators must, so far as is reasonably practicable, engage with workers. Mining and tunnelling operations must also have effective worker participation practices, regardless of the size, location, hours of operation, or method of mining. A safe workplace is more easily achieved when everyone involved in the work: > > communicates with each other to identify hazards and risks > > talks about any health and safety concerns > > works together to find solutions DUTIES UNDER HSWA AND THE MOQO REGULATIONS All PCBUs have worker engagement and participation duties under HSWA. Mine and tunnel operators have extra duties under the MOQO Regulations, as follows: > > The SSE must engage with workers and health and safety representatives (HSRs) when preparing and reviewing the health and safety management system (HSMS), including principal control plans (PCPs) and PHMPs. > > Mine and tunnel operators must document worker participation practices. > > If a worker reports the existence of a hazard, the mine or tunnel operator must: make sure the report is investigated promptly advise the worker of the result of the investigation. 14

15 SECTION 1.0 // INTRODUCTION HEALTH AND SAFETY REPRESENTATIVES An HSR is a worker elected by the members of their work group to represent them in health and safety matters. An industry health and safety representative (industry HSR) may be appointed to represent underground coal mine workers. An industry HSR is appointed by a union or by a group of underground coal mine workers. They must meet the competency and experience requirements for an HSR at a mining operation (see MOQO Regulation 110). As well as the functions and powers that all HSRs have, an industry HSR has additional functions and powers. Details of the appointment, removal or resignation of the industry HSR must be provided to WorkSafe. WorkSafe issues an identity card to the industry HSR. Trained health and safety representatives and industry HSRs can issue a notice to suspend or stop a mining operation if they believe on reasonable grounds that there is a serious risk to health and safety MORE INFORMATION ABOUT WORKER ENGAGEMENT, PARTICIPATION AND REPRESENTATION For more information on worker engagement, participation and representation see WorkSafe s website and: > > good practice guidelines Worker Engagement, Participation and Representation > > interpretive guidelines Worker Representation through Health and Safety Representatives and Health and Safety Committees. When reading the guidelines replace the following terms with the extractive industry terms: > > replace PCBU with mine or tunnel operator > > replace work group or members of a work group with a group of workers who are represented by a health and safety representative or workers in a mining or tunnelling operation > > replace business or undertaking with mining or tunnelling operation. 1.6 HEALTH AND SAFETY MANAGEMENT SYSTEM All mining and tunnelling operations must have an HSMS. It is part of the mine or tunnelling operation s overall management system. The ground or strata instability PHMP is an essential part of the HSMS. The SSE must: > > develop, document, implement and maintain the HSMS > > make sure it is easily understood and used by all workers > > engage with workers when preparing and reviewing the HSMS and when providing instruction before the workers start work at the mining or tunnelling operation. 15

16 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS 1.7 HAZARDS AND RISKS The PCBU must eliminate risks to health and safety, so far as is reasonably practicable. If it is not reasonably practicable to eliminate risks, they must be minimised, so far as is reasonably practicable. The SSE must ensure there are processes in place to: > > identify hazards (appraise risks) at the mining or tunnelling operation > > assess the risks of injury or ill-health to workers from the hazards > > identify the controls required to manage the risks. The risk appraisal could identify principal hazards; these are hazards that can create a risk of multiple fatalities in a single accident, or a series of recurring accidents, at the mining or tunnelling operation. They will either be one of ten specified hazards in the MOQO Regulations (which include ground or strata instability), or any other hazard identified during the risk appraisal that meets the definition. Unless hazards are identified and risks assessed properly, no amount of risk management will ensure a safe place and system of work. Unrecognised risks can lead to serious consequences. See section 2 where the causes of ground or strata instability are discussed. 1.8 PRINCIPAL HAZARD MANAGEMENT PLAN FOR GROUND OR STRATA INSTABILITY The ground or strata instability PHMP describes the principal hazard, records the risks of injury or ill-health to workers presented by ground or strata instability at the mining or tunnelling operation, and describes the controls that have been systematically identified to manage them. The PHMP must identify who is responsible for implementing, monitoring and documenting these controls. For detailed information, see: > > MOQO Regulations 68 and 71 > > WorkSafe s interpretive guidelines Developing a Ground or Strata Instability Principal Hazard Management Plan. 1 A PHMP for ground or strata instability must, at a minimum, address the following: (a) the circumstances in which ground or strata failure may occur (b) how potential ground or strata failure could be avoided through the design of suitable ground or strata support methods that must take into account: (i) characteristics of the area to be supported (ii) surrounding workings (iii) activities to be carried out (iv) size and geometry of the openings in underground workings 1 The interpretive guidelines include a detailed example of a format that could be used to develop a ground or strata instability PHMP. 16

17 SECTION 1.0 // INTRODUCTION (c) clear directions and diagrams for the implementation of suitable ground or strata support methods (d) continuous 2 modelling, testing, and updating, where required, of ground or strata support methods (e) appropriate equipment and procedures to monitor, record, interpret, and analyse data about seismic activity and its impact on the mining or tunnelling operation (f) collection, analysis, and interpretation of relevant geotechnical data (g) maintenance of the integrity of ground or strata support (h) allowance for higher standards of support to be installed than that required by the PHMP. Produce the PHMP in the context of the whole HSMS so that it relates to other PHMPs, PCPs, or processes and procedures that rely on the PHMP as a control. This helps to prevent gaps and identify overlaps in processes and information where it relates to ground or strata instability, or where ground or strata instability may impact other PHMPs and PCPs. Develop the PHMP using information from the geotechnical assessment gathered at the exploration and pre-feasibility stage of a project and the subsequent design, planning and ongoing operations. Complete design and stability studies using an appropriate Factor of Safety (FoS) or other appropriate risk management index or margin. Other inputs that contribute to the PHMP include: > > a review of risk appraisals and risk assessments > > incident/near miss reports > > results of reviews or audits completed > > consultation with workers > > industry or manufacturers reports, where relevant. The risk appraisal and assessment methodology used needs to be consistent with that specified in the HSMS. The PHMP needs to include the results of the ground or strata instability risk assessment. Controls need to be implemented to effectively manage the risks of harm and the level of ground support needed. The SSE must ensure the effectiveness of the controls is monitored and corrective actions taken, if required. The components involved in the development and maintenance of a ground or strata instability PHMP are shown in Figure 1. 2 In this code, continuous means over the life of the mine or tunnel. The frequency (eg daily, weekly, or monthly intervals) will be determined by the risk assessment and the design. 17

18 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS Risk appraisal of mining or tunnelling operation Mining method Geotechnical assessment Mining equipment GROUND OR STRATA INSTABILITY PHMP Review (and revision) of the PHMP Internal or external audit of the PHMP SUPPORTING DOCUMENTS Risk assessment for ground or strata instability Manager s support rules/plans Trigger action response plans Monitoring plans Hazard plans/maps Application for construction or permit to tunnel Remedial support plans Standard operating procedures Training for workers Figure 1: Development and maintenance of a ground or strata instability PHMP 3 3 Adapted from page 11: NSW Government Trade & Investment Mine Safety.(2015). NSW Code of Practice WHS (Mines) Legislation: Strata control in underground coal mines. New South Wales, Australia: NSW Department of Trade and Investment, Regional Infrastructure and Services. 18

19 PART B IN THIS PART: Section 2: Section 3: Section 4: Causes of ground or strata instability at the operation Geotechnical assessment Design of control measures/support methods to avoid ground or strata instability

20 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS PART B 02/ CAUSES OF GROUND OR STRATA INSTABILITY AT THE OPERATION IN THIS SECTION: 2.1 Identify the causes of ground or strata instability 20

21 SECTION 2.0 // CAUSES OF GROUND OR STRATA INSTABILITY AT THE OPERATION The legislation that applies to this section is: Health and Safety at Work Act 2015 Section 22 Meaning of reasonably practicable Schedule 3, clause 4 Meaning of tunnelling operation Health and Safety at Work (Mining Operations and Quarrying Operations) Regulations 2016 Regulation 3 Interpretation competent person Regulation 65 Meaning of principal hazard Regulation 67 General purposes of principal hazard management plans Regulation 68 Content of principal hazard management plans Regulation 71 Principal hazard management plans for ground or strata instability Regulation 73 Consideration of whether inundation and inrush is a principal hazard Regulation 217(1)(k) Details to be included in plans (the location of inrush control zones) 2.1 IDENTIFY THE CAUSES OF GROUND OR STRATA INSTABILITY Ground or strata instability is a principal hazard associated with mining and tunnelling operations. Some potential causes of ground or strata instability at a mining operation and tunnelling operation are listed below: > > inadequately designed ground support > > poor quality of ground support consumables > > poorly installed ground support > > deteriorated ground support > > mining induced seismicity > > natural seismicity > > excessive compressive stress around excavations > > excessive shear stress on discontinuities > > tensile forces around excavations resulting from strata relaxation > > ground water or artificially introduced water > > presence of adverse geological structures in immediate vicinity of excavation > > inappropriate choice of excavation or mining method > > loose blocks due to poor rock mass quality in the perimeter of the excavation > > collapse from localised or general thawing, or ineffective freeze due to moving ground water (ground freezing) > > excessive blast damage to the perimeter of the excavation > > inappropriate shape and size of pillars, roadways or roadway alignment > > pillar failure or collapse due to undersized pillars or poor mine layout > > load transfer, abutment stress, periodic weighting, face slabbing. Identify, assess and detail the risks in the risk appraisal and risk assessment that forms part of the PHMP. For more information see section

22 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS STRESS A competent person must analyse the stress environment at the mining or tunnelling operation. This should include an assessment of the three-dimensional (3D) stress field across the relevant extent of the mining or tunnelling operation to develop an understanding of the magnitude and direction of the stress field, and any apparent variability present. This may be undertaken by a programme of in situ measurements, complemented by stress change monitoring during excavation, together with stress mapping and an awareness of stress conditions in adjacent operations, if present. This assessment informs the excavation and support design. Options to measure stress in mining or tunnelling operations may include: > > in situ stress measurements > > stress change monitoring > > acoustic emission testing plus variation GEOLOGICAL HAZARDS Some geological hazards encountered in excavations contribute to other principal hazards. Obtain specialist advice from a competent person if there is any indication of the presence or potential existence of one or more of the following hazards: > > significant water inflow > > gas outburst > > rock outbursts > > thermal activity > > discontinuity SEISMIC ACTIVITY Under MOQO Regulation 71(2)(e) the PHMP must address the appropriate equipment and procedures to monitor, record, interpret and analyse data relating to seismic activity and its impact on the mining or tunnelling operation. Natural seismicity is an earthquake that is caused through natural earth processes and needs to be considered in mine or tunnel design. Understanding the location and seismic hazard profile of major fault zones capable of producing strong ground motions at the mine or tunnel site is important. The competent person considers this when undertaking the geotechnical review. The potential for earthquakes may need to be factored into the design, both during excavation and construction, as well as the final tunnel or roadway formation. Mining-induced seismicity occurs as a result of stress redistribution around underground openings. In some cases, such stress changes may trigger a sudden slip on a fault. This is almost always accompanied by ground vibration which may cause considerable damage to underground openings. In other cases, abutments or pillars may become overloaded and yield suddenly. During the construction of tunnels, which can be of relatively short-term duration, the seismic risk may range from very low to moderate. When the tunnel construction, enlargement or extension has been completed the tunnel will no longer be a tunnelling operation by definition under HSWA Schedule 3, clause 4. The permanent tunnel must be designed for seismic loads in accordance with the New Zealand Building Code. 22

23 PART B 03/ GEOTECHNICAL ASSESSMENT IN THIS SECTION: 3.1 Requirement for a geotechnical assessment at mining and tunnelling operations 3.2 Site characterisation 3.3 Collection, analysis and interpretation of geotechnical data 3.4 Re-using a geotechnical assessment 3.5 Review of the geotechnical assessment 23

24 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS The legislation that applies to this section is: Health and Safety at Work (Mining Operations and Quarrying Operations) Regulations 2016 Regulation 3 Interpretation competent person Regulation 11 Mine operator must ensure site senior executive has sufficient resources Regulation 69 Review and revision of principal hazard management plans Regulation 71 Principal hazard management plans for ground or strata instability 3.1 REQUIREMENT FOR A GEOTECHNICAL ASSESSMENT AT MINING AND TUNNELLING OPERATIONS The SSE must ensure that a competent person completes a geotechnical assessment to determine the level of ground or strata reinforcement required to safely conduct the mining or tunnelling operation. When completing the geotechnical assessment obtain input from the relevant technical disciplines (eg mining engineers, geotechnical engineers, civil engineers, geophysicists, surveyors, geologists, and hydro-geologists). The completed geotechnical assessment should be recorded, dated and signed by the competent person carrying out the assessment COMPONENTS OF A GEOTECHNICAL ASSESSMENT The geotechnical assessment should cover proposed activities over the whole life of the mine or tunnel, from the feasibility study stage, operation of the mine or tunnel, to the final closure and abandonment of the mine or the full life of the tunnel. The SSE needs to ensure the geotechnical assessment clearly defines the area the assessment relates to and the resulting ground control system design limited to that area. The components of the geotechnical assessment and the outputs of that analysis are illustrated in Figure 2. They include: > > Site characterisation of the ground to be supported, including natural and geotechnical features such as: lithology, seam thickness/orebody shape, stratigraphic variability, seam dip, depth of cover, geological structure including faults, bedding, joints rock properties measurement or assessment of rock stress magnitude and orientation, including excavation, pre-mining and mining-induced conditions and areas of high in situ stress presence of water (eg aquifers, likely heads of pressures, water quality, inflows of water) air temperature and humidity, gas inflows, and other variability in the rock (eg presence of contaminated ground) hot groundwater or rock (geothermal) earthquake potential, depending on the location of the operation in relationship to fault lines 24

25 SECTION 3.0 // GEOTECHNICAL ASSESSMENT obstructions, both man-made and natural information about surrounding workings, including abandoned or previously excavated workings > > analysis and formulation of a geotechnical model, including definition of geotechnical domains, to classify volumes of rock with similar geotechnical properties and behaviours > > identification of failure processes and mechanisms > > ground support design using an appropriate Factor of Safety (FoS) or other appropriate risk management index or margin, including: design of pillar and barrier sizes design of mine or tunnel layouts including extraction/mining methodology design of ground support for all stages of the operation development, extraction, and closure design of the size, shape and orientation of openings > > development of a minimum ground support standard for each excavation type and geotechnical domain > > development of trigger action response plans (TARPs) for each excavation type > > identification of suitable monitoring systems, such as design verification monitoring and testing, routine monitoring, and requirements for seismic activity monitoring, where appropriate. Consider the following in the geotechnical assessment: > > experiences from other local and/or equivalent mining or tunnelling operations, where applicable > > the mining method, mining direction, gradients, excavation sequence > > interdependencies between ground control design issues and other key aspects of design, such as inundation, ventilation and the management of subsidence. The assessment may re-use relevant geological and geotechnical information previously collected as part of the feasibility studies or previous excavations, including: > > the results of further testing > > specific assumptions about the life of the mine or tunnel > > intended mining or tunnelling methods > > existing and proposed activities > > extraction rates. 25

26 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS GEOTECHNICAL ASSESSMENT (Inputs and Outputs) Site Characterisation a. Collect data (site investigation) Mapping, geophysics Drilling logging, sampling downhole geophysics and sampling Determine in situ stress field Ground water studies (hydrogeology) Laboratory testing of samples Exploration adits b. Process data/analyse Create geological model (seam/ore body shape, thickness, depth, dip, geological structures, lithology) Classify rock into domains (or mass types). Analyse laboratory results Review other operations Review relevant experience from local/ equivalent mining/ tunnelling operations Mining/Excavation method Type of mining Excavation dimensions Identification of the core geotechnical risks associated with the particular method chosen Life of mine or tunnel Surrounding workings Define abandoned/ previously worked areas Other factors Subsidence constraints Ventilation requirements Flitting distances Assess likely failure mechanisms Define acceptable level of risk for the support/pillar design (eg FoS) Consider acceptable stability criteria eg geological duty life-span required etc. What is the end result sought? Select appropriate method of stability analysis (or design) (empirical, numerical, analytical) Pillar design Extraction/stoping design Rock reinforcement design Outputs of analysis Levels of ground/strata support required to safely conduct the operation DESIGN Dimensions of pillars/ ribs/mine layout Extraction sequence/ dimensions Level of rock reinforcement required for excavations eg bolt capacity, length, density, spacing etc. Requirements for secondary support needed before extraction or stoping Other outputs of analysis: > required design verification > routine monitoring requirements monitoring devices, appropriate triggers for TARPs > other testing pull testing, encapsulation testing etc Figure 2: Components of the geotechnical assessment and design outputs 26

27 SECTION 3.0 // GEOTECHNICAL ASSESSMENT 3.2 SITE CHARACTERISATION Site characterisation provides an understanding of the physical characteristics of the rock mass to enable the design of ground support. Stages of site characterisation include: > > review of regional geology and information gathered earlier as part of feasibility studies > > site investigation > > lab testing > > preparation of a geological model > > interpretation of geotechnical and geophysical data to define soil and rock parameters for use in ground support design > > classification of rock mass into geotechnical domains. Characterisation data is gathered from drilling logs or cores, observation, sampling, testing and analysis of a range of information and data about the ground, and other physical characteristics of the natural environment of the mining or tunnelling operation. This informs the geotechnical assessment. Characterisation provides an estimate of rock mass strength and the in situ stress environment, to enable the prediction of how the ground will respond to the effects of excavation. It also provides information on the rock mass variability, including the impact of lithological changes and geological anomalies such as faults and dykes, and risks associated with seismicity. 4 Ongoing updating and recalibration of the geological/geotechnical model is required throughout the operating stage. The mine or tunnel operator must ensure the SSE has adequate resources for site investigations to effectively assess ground control risks. 3.3 COLLECTION, ANALYSIS AND INTERPRETATION OF GEOTECHNICAL DATA The PHMP must address how relevant geotechnical data will be collected, analysed and interpreted, including the monitoring of openings and excavations, where appropriate. The mining or tunnelling operation should have a database of geological and geotechnical data that is regularly updated as new data is acquired. This data includes: > > geological/geotechnical logging records (eg downhole geophysics, core photographs) > > geotechnical test results and rock mass properties (eg uniaxial compressive strength, fault/defect properties, shear strength and modulus as required) GEOLOGICAL/GEOTECHNICAL MODEL The mine or tunnel operator needs to have a geological/geotechnical model with regularly updated information, including: > > geological structure > > geological boundaries 4 Adapted from page 11: NSW Government Trade & Investment Mine Safety.(2015). NSW Code of Practice WHS (Mines) Legislation: Strata control in underground coal mines. New South Wales, Australia: NSW Department of Trade and Investment, Regional Infrastructure and Services. 27

28 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS > > seam/ore body grid models or 3D models > > overburden/host rock grid models or 3D models > > rock mass classification GEOTECHNICAL MAPPING Geotechnical mapping needs to be regularly done in all active and accessible excavated areas. This includes: > > face mapping > > structural mapping > > geotechnical conditions observations or inspections > > excavation behaviour reports > > evidence of stress through deformation/failure mapping REPORTING OF GEOTECHNICAL INFORMATION Standard operating procedures (SOPs) need to be developed to support regular reporting of geotechnical information by the relevant workers to the mine or tunnel manager and other workers. The mine or tunnel operator needs to retain evidence of this reporting. 3.4 RE-USING A GEOTECHNICAL ASSESSMENT Where an existing design has already been proven, it may be used as a basis for the design of ground control measures for a new operation in the same area, provided that: > > the ground conditions at both operations are in the same domain or are not significantly different, and > > the excavation method is the same. Sufficient site investigation should be carried out to confirm that the ground conditions at the new excavation are similar to those at the previous operations. Mine or tunnel operators need to complete a geotechnical model verification to compare old with new ground conditions. If ground conditions are confirmed as being similar, the information from these previous operations may be used. References to any earlier assessments must be included. 3.5 REVIEW OF THE GEOTECHNICAL ASSESSMENT The SSE must ensure that the PHMP is reviewed at least once every two years after the date the PHMP was initially developed, being the date it was initially approved by the SSE, or as when required under the circumstances listed in MOQO Regulation 69(2). Assumptions from the geotechnical assessment must be checked against what has actually happened with the ground. See MOQO Regulations 71(2)(d),(e) and (f). Events that can trigger a review of the geotechnical assessment and review of the ground or strata instability PHMP include the following: > > a major change in the ground conditions encountered conditions outside the site characterisation or the assumptions used for the design in the geotechnical assessment 28

29 SECTION 3.0 // GEOTECHNICAL ASSESSMENT > > monitoring information that indicates the ground is not behaving as predicted in the geotechnical assessment > > a change in the mining method > > a change in the mining sequence > > a major change in the mine or tunnel layout > > a major change in the equipment used to install ground support such that the design specified in the geotechnical assessment cannot be implemented > > a major change in ground support type > > a significant accident involving ground instability. See section 10 for information on review and audit. 29

30 PART B 04/ DESIGN OF CONTROL MEASURES/ SUPPORT METHODS TO AVOID GROUND OR STRATA INSTABILITY IN THIS SECTION: 4.1 Design details and support methods 4.2 Design methodologies used to determine ground support needed 4.3 Design requirements for rock reinforcement systems 4.4 Stope or pillar design requirements for coal and metalliferous mines 4.5 Temporary and permanent ground support systems 4.6 Primary and secondary support systems 4.7 Temporary support systems 4.8 Shafts 4.9 Continuous modelling and design verification 30

31 SECTION 4.0 // DESIGN OF CONTROL MEASURES/SUPPORT METHODS TO AVOID GROUND OR STRATA INSTABILITY The legislation that applies to this section is: Health and Safety at Work (Mining Operations and Quarrying Operations) Regulations 2016 Regulation 3 Interpretation shaft Regulation 71 Principal hazard management plans for ground or strata instability Regulation 117 Installation of ground or strata support 4.1 DESIGN DETAILS AND SUPPORT METHODS The design details and support methods are outputs of the geotechnical assessment. The excavation design and the systematic installation of suitable support of openings during excavation are the primary controls to prevent ground or strata instability occurring at a mining or tunnelling operation. Components of the design include some or all of the following: 5 > > limits of extraction > > excavation dimensions > > pillar sizes > > type and spacing of support or reinforcement density; typically this will take the form of a support plan > > specifications for any material or equipment forming part of any ground control system, including quality and capacity verification testing > > timing of installation of the support or reinforcement > > proposed method of work (mining method and its compatibility with support systems) > > procedures for dealing with material changes in conditions (ie conditions that are more adverse or favourable) such as TARPs > > information on other risks such as known zones of weakness or proximity to other workings > > rationale for sequencing extraction and filling (if appropriate) > > backfill that provides confinement for roof/backs and ribs. The designed or selected control measures must be able to be implemented without unnecessary risks to any person during the installation, operation and abandonment of the mine or tunnel DESIGN DOCUMENT Include the geotechnical assessment in the design document. A competent person should sign the design document. For tunnelling operations, a producer statement (PS1) 6 should be signed by the designer. These documents form the basis of the manager s support rules. Include the manager s support rules as part of the PHMP. Technical specifications need to be prepared for all ground support products or components of the system used at the mining or tunnelling operation, such as load capacities (support resistance) and energy absorption capacities. These technical specifications need to be included in the PHMP. 5 Adapted from page 11: Health and Safety Executive (HSE) (2015) Guidance on Regulations: The Mines Regulations Retrieved from: 6 A PS1 (Producer Statement 1) confirms that design work has been carried out by a competent design professional and is expected to comply with the relevant legislation. 31

32 EXTRACTIVES: GROUND OR STRATA INSTABILITY IN UNDERGROUND MINES AND TUNNELS 4.2 DESIGN METHODOLOGIES USED TO DETERMINE GROUND SUPPORT NEEDED A competent person needs to apply an appropriate design methodology (during the geotechnical assessment) to determine the level of ground support required to safely conduct the mining or tunnelling operation, including roadways, pillar or tunnel design and ground reinforcement requirements. The competent person needs to use an appropriate FoS, or other appropriate risk management index or margin, depending on the duty and lifespan of the mine or tunnel opening. For example, the support system for an excavation planned to be open for a short time may be designed to a lower FoS than a roadway that needs to be stable for the entire life of the mine or tunnel. The design methodologies are generally empirical, analytical or numerical analyses. These methodologies apply to both mining and tunnelling operations EMPIRICAL METHODS Empirical design methods are design approaches and formulations developed from statistical analysis of controlled, quantified databases of experience on real-world projects. The approach relies on comparing the experiences of past practices to predict future behaviour based upon the factors most critical for the design. Empirical methods are reliant on credible databases. Note that: > > The risk-based parameters quoted for a particular database and design system are unique to that system. They are not to be applied to other applications without due consideration. > > An understanding of the origins, nature and limitations of the database is important. Uncertainty increases towards the boundaries of the database. Particular caution should be adopted in attempting to apply the results of an empirical study outside the range of the underpinning database. An example of an empirical design method is the use of rock mass classification methods calibrated against large databases to provide guidelines for support design or cavability. Determining the rock class, span of the opening and rock mass quality will provide guidance as to the reinforcement category required and, if applicable, support system for a particular set of characteristics ANALYTICAL METHODS Analytical design methods apply equations developed from basic mechanistic or engineering principles to the analysis of ground behaviour, so that when controls are applied, design outcomes can be expressed numerically (eg FoS). These design methods typically require input parameters measured in the laboratory and/or field. An example of an analytical design method is the calculation of a dead weight load and the associated design of support to carry that load. 32

33 SECTION 4.0 // DESIGN OF CONTROL MEASURES/SUPPORT METHODS TO AVOID GROUND OR STRATA INSTABILITY A disadvantage of analytical models is that it is rare for a design problem to involve one mode of behaviour or failure only. Stress and deformation are generally more complex, with multiple potential failure modes or varying ground loads. Most geotechnical design problems have input parameters that are not fully defined, either in terms of the expected value or the degree of variability. Engineering judgement is required, with a link to actual experience to provide design calibration NUMERICAL METHODS Numerical design methods involve a range of different underpinning capabilities, referred to as constitutive equations, used to describe the type of rock behaviour and potential failure criteria. The numerical code selected needs to have the capabilities that are applicable to the geotechnical environment being modelled; otherwise results will potentially be incorrect and could be misleading. Modelling accuracy is highly dependent on input parameters that typically require extensive, high-quality site investigations and laboratory testing. Numerical models should address: > > calibration to real-world experience/empirical outcomes > > sensitivity analysis to test the model s rationale > > the results of comparisons with the outcomes of alternative design methodologies DESIGN REQUIREMENTS FOR ROCK REINFORCEMENT SYSTEMS The design of rock reinforcement systems needs to consider: > > if the design is capable of being implemented without undue risk to any worker > > the prevailing geotechnical hazards and mining abutment effects over the life of the excavation, as well as taking account of other non-geotechnical operational constraints > > the profile, use and anticipated life cycle of the opening/roadway, leading to determination of appropriate support methodologies, materials and installation equipment > > the timing of both primary and any secondary support installation. This needs to be assessed relative to the prevailing geotechnical environment and likely impact on stability > > whether the support design methodologies selected and justified for each application are applicable to the expected ground behaviour and potential failure mechanisms > > establishing the protocols for confirming appropriate quality and adequacy of support materials and control systems for validating installation practices. The complex nature of reinforcement design requirements means design methods should not be relied upon in isolation but considered as interdependent on each other. Reinforcement design should not rely on one single strategy, or expect only one single failure mode, especially in critical excavations. Rock failure is usually multi-modal and complex. 7 Adapted from page 19: NSW Government Trade & Investment Mine Safety. (2015). NSW Code of Practice WHS (Mines) Legislation: Strata control in underground coal mines. New South Wales, Australia: NSW Department of Trade and Investment, Regional Infrastructure and Services. 33